A carboxylate-bridged Ni8II cluster with a distorted cubane topology: structure, magnetism and density functional studies

Using a dicarboxylate ligand appended with (2-pyridyl)ethylamine unit, a new cluster [Ni-8(II)(L-4)(6)-(DMF)(2)(CH3OH)(2)(H2O)(6)][ClO4](4)center dot 2CH(3)OH center dot 2CH(3)CO(2)C(2)H(5) (1) [L-4(2-): 3-[N-{2-(pyridin-2-yl)ethyl}amino]bis(propionate)] has been synthesized, through 'coordination-driven self-assembly'. The crystal structure of 1 reveals a centrosymmetric octanuclear carboxylate-bridged nickel(II) tetracation, with a distorted cubane topology. The four crystallographically independent nickel(II) centres differ markedly in their coordination environment. Magnetic studies (2-300 K) reveal that in 1 the net magnetic-exchange is antiferromagnetic. Based on geometric parameters associated with two interacting nickel(II) centres, six magnetic-exchange coupling constants (J values) were considered for magnetic data analysis. Notably, 1 provides the first example of a Ni-8(II) cluster (i) bridged solely by carboxylates in three bridging modes (monatomic, syn-anti and anti-anti), (ii) exhibiting four ferromagnetic and two antiferromagnetic magnetic-interactions and (iii) demonstrating a good agreement between six J values (obtained from experimental data analysis) and those obtained from DFT calculations, at the B3LYP-level of theory.